The present invention concerns an injection syringe of the type which includes, on the one hand, an elongate syringe body comprising a tube and a front wall equipped with an injection needle, and, on the other hand, a rear actuating plunger which is mounted so as to be displaceable in the tube, and in which the injection needle continues axially inside the syringe body as far as a rear end, away from which is initially arranged, in the syringe body, at least one perforable transverse wall, the needle and the transverse wall being displaceable relative to one another from an initial position in which the transverse wall is away from the needle as far as a final position in which the transverse wall is pierced by the said needle.
The perforable transverse wall is, for example, carried by the actuating plunger.
In a variant, the transverse wall is for example formed by an intermediate plunger arranged in the syringe body between the rear end of the needle and the actuating plunger. The intermediate plunger then delimits, with the actuating plunger, a housing in which the fluid to be injected is contained.
In the latter case, when the actuating plunger is driven in, the intermediate plunger is perforated by the rear end of the needle in order to allow the fluid to flow through the needle.
If the section of the needle projecting inside the syringe body is long, the intermediate plunger risks being perforated with a slight angular and/or axial offset relative to the axis of the syringe body, because of the low rigidity of the needle.
Under these conditions, at the end of injection, when the actuating plunger comes into contact with the intermediate plunger and pushes it forwards with the view to moving it along the internal section of the needle, the offset existing between the axis of the needle and the axis of the syringe makes it difficult to move the intermediate plunger along the latter and risks leading to obstruction.
Similar problems are encountered when the transverse wall is carried by the front end of the actuating plunger and constitutes the front face of the latter.
The object of the invention is to make available a solution to the malfunctions of the syringe resulting from an angularly and/or axially offset perforation of the transverse wall by the rear end of the needle.
To this end, the subject of the invention is an injection syringe of the aforementioned type, characterized in that it includes rigid means for axial guiding of the rear end of the needle during the perforation of the transverse wall.
The rigid means for axial guiding of the rear end of the needle hold in position the part of the needle projecting inside the syringe body, so that the latter perforates the transverse wall along the common axis of the needle of the syringe, avoiding the obstruction problems mentioned above.
The subject of the invention is furthermore a needle holder assembly including a wall integral with an injection needle passing through the said wall, as well as a mobile protector of the injection end of the needle, displaceable relative to the needle between a retracted position behind the injection end of the needle and an active protection position in which the front end of the protector is in front of the injection end of the needle, which protector has legs which pass through the said body and extend along the said needle, characterized in that it includes a rigid member for axially guiding the rear end of the needle, which rigid axial guiding member is carried by the free ends of the legs of the protector.